FIG. 1 is a schematic diagram of a vertically oriented optical voltage and electric field sensor wherein light travels and a voltage or electric field is applied in a direction of &lt;100&gt;. In the figure, the numeral 1 indicates an optical fiber, 2 is a rod lens, 3 is a polarizer, 4 is a quarter-wave plate, 5 is a BSO or BGO device, 6 is an analyzer and 7 is an input voltage source. The following description is directed to a BSO device, it being indicated that the same explanation applies to a BGO device.
After falling on optical fiber 1, light passes through rod lens 2, polarizer 3 and quarter-wave plate 4, and falls on BSO device 5 having a transparent electrode formed on front and back sides. The light is polarized according to the voltage level applied to BSO device 5 from input voltage source 7 through the electrodes. The sensor uses the change in polarized state to detect the intensity of the input voltage or electric field.
FIG. 2 shows a BSO device 8 and an input voltage source 7 in a horizontally oriented optical voltage and electric field sensor configuration wherein light travels in a direction of &lt;100&gt; whereas a voltage or electric field is applied in a direction of &lt;110&gt;. The other components of the sensor are identical to those illustrated in FIG. 1.
FIG. 3 is a frequency characteristic curve for the modulation sensitivity of a conventional optical voltage and electric field sensor using a BSO device. When the frequency of the voltage or electric field applied to a conventional sensor is increased, piezoelectric effect occurs at certain frequencies and mechanical resonance develops in the BSO device. The resulting mechanical stress affects the refractive index of the BSO device. In consequence, as shown in FIG. 3, the frequency characteristic curve for the modulation sensitivity of a conventional sensor has very high peaks a, b and c at certain frequencies. Therefore, the conventional sensor cannot be used, in analysis of a phenomenon such as high-voltage surge that requires a constant modulation sensitivity up to high frequency components.